diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index da521dbc535..bf7469093a8 100644
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -252,7 +252,7 @@ namespace llvm {
 
     /// addKillFlags - Add kill flags to any instruction that kills a virtual
     /// register.
-    void addKillFlags();
+    void addKillFlags(const VirtRegMap*);
 
     /// handleMove - call this method to notify LiveIntervals that
     /// instruction 'mi' has been moved within a basic block. This will update
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index bdf4f2dfffc..b447c3c2d70 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -34,6 +34,7 @@
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "LiveRangeCalc.h"
+#include "VirtRegMap.h"
 #include <algorithm>
 #include <limits>
 #include <cmath>
@@ -733,12 +734,28 @@ bool LiveIntervals::shrinkToUses(LiveInterval *li,
 // Register allocator hooks.
 //
 
-void LiveIntervals::addKillFlags() {
+void LiveIntervals::addKillFlags(const VirtRegMap *VRM) {
+  // Keep track of regunit ranges.
+  SmallVector<std::pair<LiveInterval*, LiveInterval::iterator>, 8> RU;
+
   for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
     unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
     if (MRI->reg_nodbg_empty(Reg))
       continue;
     LiveInterval *LI = &getInterval(Reg);
+    if (LI->empty())
+      continue;
+
+    // Find the regunit intervals for the assigned register. They may overlap
+    // the virtual register live range, cancelling any kills.
+    RU.clear();
+    for (MCRegUnitIterator Units(VRM->getPhys(Reg), TRI); Units.isValid();
+         ++Units) {
+      LiveInterval *RUInt = &getRegUnit(*Units);
+      if (RUInt->empty())
+        continue;
+      RU.push_back(std::make_pair(RUInt, RUInt->find(LI->begin()->end)));
+    }
 
     // Every instruction that kills Reg corresponds to a live range end point.
     for (LiveInterval::iterator RI = LI->begin(), RE = LI->end(); RI != RE;
@@ -749,7 +766,32 @@ void LiveIntervals::addKillFlags() {
       MachineInstr *MI = getInstructionFromIndex(RI->end);
       if (!MI)
         continue;
-      MI->addRegisterKilled(Reg, NULL);
+
+      // Check if any of the reguints are live beyond the end of RI. That could
+      // happen when a physreg is defined as a copy of a virtreg:
+      //
+      //   %EAX = COPY %vreg5
+      //   FOO %vreg5         <--- MI, cancel kill because %EAX is live.
+      //   BAR %EAX<kill>
+      //
+      // There should be no kill flag on FOO when %vreg5 is rewritten as %EAX.
+      bool CancelKill = false;
+      for (unsigned u = 0, e = RU.size(); u != e; ++u) {
+        LiveInterval *RInt = RU[u].first;
+        LiveInterval::iterator &I = RU[u].second;
+        if (I == RInt->end())
+          continue;
+        I = RInt->advanceTo(I, RI->end);
+        if (I == RInt->end() || I->start >= RI->end)
+          continue;
+        // I is overlapping RI.
+        CancelKill = true;
+        break;
+      }
+      if (CancelKill)
+        MI->clearRegisterKills(Reg, NULL);
+      else
+        MI->addRegisterKilled(Reg, NULL);
     }
   }
 }
diff --git a/lib/CodeGen/VirtRegMap.cpp b/lib/CodeGen/VirtRegMap.cpp
index a1cac7c5b2a..6343e8a3529 100644
--- a/lib/CodeGen/VirtRegMap.cpp
+++ b/lib/CodeGen/VirtRegMap.cpp
@@ -200,7 +200,7 @@ bool VirtRegRewriter::runOnMachineFunction(MachineFunction &fn) {
   DEBUG(VRM->dump());
 
   // Add kill flags while we still have virtual registers.
-  LIS->addKillFlags();
+  LIS->addKillFlags(VRM);
 
   // Live-in lists on basic blocks are required for physregs.
   addMBBLiveIns();